Anatomy of roots

The root is responsible for attaching a plant to the ground, providing support, and initiating the absorption of water and nutrients from the soil. They are cylindrical, underground parts of the plant, which consist of endogenous lateral branches. They are known as negatively phototropic and positively geotropic. 

The formation of roots takes place from the radical part of the embryo, which is in its developing stage. The anatomical structure of the root comprises several tissues and different types of cells. 

There are two types of roots – monocot roots and dicot roots.

Anatomy Of Dicotyledonous Root

Dicot roots belong to dicot plants (with two cotyledons in the seed). The anatomy of the dicotyledonous root is as follows:

Epidermis

The epidermis is the outermost layer of the root, referred to as the epiblema, piliferous, or rhizodermis layer. This layer is composed of parenchymatous cells. In this layer, unicellular root hairs are present, formed by the elongation of specific cells in the maturation zone, which helps in the absorption of water. Here, stomata and cuticles are not present.

Cortex

The layer present between the epidermis and endodermis is referred to as the cortex. The cells in this layer are circular, with some intercellular spaces that help move water and other substances easily. The cells here are homogenous parenchyma cells.

Endodermis

It is the innermost layer of the cortex, present between the cortex and pericycle. It is a single layer that is composed of barrel-shaped cells. It is seen that the radial walls and tangential walls of the endodermis consist of Casparian strips, which are made up of waxy material called suberin. It is known to give the hydrophobic feature to this layer of the root. Endodermis consists of transfusion cells or passage cells that aid in the passage of water from the cortex towards the pericycle.

Pericycle

The layer that is present after the epidermis is the pericycle. It is composed of parenchyma cells. In dicots, a pericycle can be either of a single layer or several layers. Secondary growth of the dicot roots occurs with the help of this layer. The cells of the pericycle gradually become meristematic. These cells then join the cambial ring, resulting in the formation of the cambium.

Vascular bundles

Vascular bundles are composed of phloem and xylem. The xylem is arranged in a way that the metaxylem is towards the centre, and the protoxylem lines are at the periphery. This type of arrangement is called an exarch. Also, the xylem and phloem are concentrated in radial arrangement, i.e., along the radii, consisting of a layer of conjunctive tissue between them. 

Pith

Pith is present in the centre and is composed of parenchymatous cells with intercellular spaces. It is not very well developed in dicot roots, as it is inconspicuous and small in size.

Anatomy Of Monocot Root

Monocot roots are present in monocot plants (with only one cotyledon in the seed). Both types of roots have some similar characteristics, but they also tend to have a few differences. The anatomy of the monocot root is as follows:

Epidermis

The epidermis of monocot root is similar to dicot root, consisting of parenchyma cells and root hairs to absorb water and minerals. 

Cortex

Monocot roots have a wider cortex compared to the dicot roots, and it lacks hypodermis. The layer consists of many parenchyma cells responsible for storing food and giving protection.

Endodermis

The endodermis is considered the innermost layer of the cortex, consisting of cells in the shape of barrels. It doesn’t contain Casparian strips.

Pericycle

Since cambium is absent in monocot roots, pericycle is known to form the lateral roots. It is a persistent layer. Monocots may have a pericycle, which can be either of a single layer as in maize or multilayer as in smilax.

Vascular bundles

The number of xylem and phloem in the monocot root is more compared to that of the dicot roots. Here, they are arranged in radial geometry. They do not contain vascular cambium. They are closed and do not possess any secondary growth. In monocots, it is known that phloem parenchyma is absent, and the phloem consists of companion cells, sieve tubes, and phloem fibres. 

Pith

In the monocot roots, the pith is well-developed, which is the opposite of the dicot roots. It is conspicuous and large.

Conclusion

Roots are thus considered a crucial part of the plant. They are known to benefit from plants and humans in a number of ways. They help provide water and minerals to the plant by absorbing them from the soil to encourage the growth and development of all parts. They help attach the plant to the soil firmly and strongly. In some plant families, roots help in the storage of food. The roots also encourage and support the life of other organisms that grow in the soil by maintaining a symbiotic relationship with them. For humans, the roots are a source of food like radish, turnip, beetroot, etc. They are also known as a vital source for many drugs and medicines, such as ginseng and ashwagandha, which are beneficial to human health.